The invention relates to a drive mechanism for a down draft vent system, in particular for a vertically directed, retractable down draft vent system, which can be moved between an extended position and a lowered position by means of a drive motor. The down draft vent system can be used with cookers or cooktops.
The down draft vent system which can be operated with the drive mechanism is a so-called cooktop ventilator which is also designated as a downdraft system. In these systems an open framework with a down draft inlet opening is arranged behind the cooktop. This open framework can be moved between a rest position and an operating position. In the rest position the open framework is retracted behind the cooktop and its upper side ends flush with the surface of the cooker. In the operating position, the open framework is driven out by a certain height from the surface of the cooker and the down draft inlet opening is thus located at a corresponding height above the cooktop.
Such a down draft vent system is described, for example, in DE 40 09 326 A1. In this down draft vent system the movement of the open framework is accomplished by means of a slider which is guided in a rail and by means of a helical cable which executes a longitudinal movement during a rotary movement of the drive motor. Provided at the ends of the rail in which the slider is guided are limit switches which switch off the drive motor on contact with the slider. The slider is not connected to the open framework but merely supports this at the bottom. During a vertical upward movement of the slider in the rail, the open framework is thus driven out above the surface of the cooker and on reaching the end position, that is the operating position, the drive motor is switched off by means of the upper limit switch. When the open framework is moved from the operating position, this is accomplished by a vertical downward movement of the slider in the rail. In this direction of movement, also the motor is switched off as soon as the end position, that is the rest position, was reached.
If an obstacle, for example, a pan is located between the upper edge of the open framework and the top of the cooker during the down movement of the open framework, the slider travels in the rail as far as its end position whereas the open framework which is guided independently of the rail, remains in a slightly elevated position until the obstacle is removed. After the obstacle has been removed, the open framework returns to the rest position as a result of its own weight.
The disadvantage with this drive mechanism is that when an obstacle occurs during extension of the open framework, if a pot for example is standing on the open framework, the open framework is nevertheless moved further and travels into its operating position.